The use of industrial robots for the flexible automation of industrial processes has become increasingly common for replacing time consuming, monotonous and difficult work. Such work can, for example, be transferring confectionary products such as chocolate or similar fragile or small objects from a conveyor belt to places in predetermined locations in, for example, boxes, with high speed and precision where the object is moving on a separate conveyor belt. The ability to be able to handle small and delicate objects effectively with great speed and precision is much sought after in the automation of industrial processes.
Delta type robots (also known as parallel robots) have applications in diverse industries, for example in the food industry and the pharmaceutical industry. The delta robot was first developed in 1985 by R. Clavel and is described in U.S. Pat. No. 4,976,582 (Clavel). Delta robots have proven their worth in particular for packaging lightweight foods, since they permit extremely high speed and high accuracy for performing pick-and-place applications, such as may be effectively used in the packaging machine industry, for picking products from a conveyor belt and placing them in cartons. Delta robots are typically parallel robots with three degrees of freedom (3 DoF), and with simpler, more compact structure and favorable dynamic characteristics.
The delta robot is a parallel robot, i.e. it consists of multiple kinematic chains, e.g., middle-jointed arms connecting a base with the end-effector. The key concept of the delta robot is the use of parallelograms which restrict the movement of the platform on which the end-effector is mounted to pure translation, i.e. only movement in the X, Y or Z direction with no rotation. The robot's base is mounted above the workspace. A plurality of actuators, e.g., three motors, are mounted equidistantly to the base. From the base, three middle-jointed arms extend. The ends of these arms are connected to a small platform. Actuation of the middle-jointed arms will move the platform along the X, Y or Z direction. Actuation can be done with linear or rotational actuators, with or without reductions (direct drive). Since the actuators are all located in the base, the middle-jointed arms can be made of a light composite material. As a result of this, the moving parts of the delta robot have a small inertia. This allows for very high speed and high accelerations. Having all the arms connected together to the end-effector increases the robot stiffness, but reduces its working volume. Each middle-jointed arm is comprised of an upper arm and a pivotally attached lower arm. Each lower arm is formed of two parallel rods that form a parallelogram. Because the lower arm consists of two parallel rods, the end effector always moves, parallel to the base plate located thereabove. This is also known as parallelogram-based control, or parallel kinematics. Note that at least three sets of the arms are necessary to provide generally translation-only motion of the end effector through three dimensions.
In use, a delta robot may be suspended over a conveyor type system to grasp and move small objects rapidly and with a high rate of precision. The end effector is arranged to support a tool or other device for carrying out a particular function or task. By a swivelling of the actuators, the end effector can be maneuvered in three-dimensional space formed by the X, Y, and Z axes to any desired position of the available work space. In addition, the end effector of the delta robot is usually equipped with visual guidance capability so that objects moving along a conveyor may be identified for picking and placing into cartons, cases, etc.
A fast movement over a relatively great distance, namely the width of the conveyor belt, requires a fast movement of several arms. This is possible in practice only if the robot arms have a low mass inertia, which in the case of delta robots is achieved through the use of light-weight materials, so that the mass inertia of the delta robot is minimized. However, the use of light-weight materials in the construction of the delta robot considerably restricts the load to which the delta robot can be subjected, which means that the delta robot can be used only for gripping light objects with a light gripper. For this reason, its useability and practical application is limited. Use of more robust parts and components would provide capability for gripping heavier objects, however such a benefit comes at the cost of a reduction in speed due to higher mass inertia. Also, light-weight materials used in the construction of delta robots tend to be less robust and cannot provide continuous production cycle times, e.g., 24-hour cycle times. Also, many light-weight materials cannot provide the benefits of low maintenance and infrequent repair as more robust parts and components that are utilized in other types of industrial machinery.
Generally, in the foodstuffs industry or in pharmaceutical applications, it is important that components of the delta robots be capable of being cleaned easily. For example, delta robots may include many parts, e.g., arms, located in proximity to the foodstuffs such as raw chicken parts being conveyed. During operation, these parts cannot be shielded from the chicken parts, making wash-down and clean-up of a delta robot a time consuming and expensive task. It would be an improvement within the art to provide an industrial robot where parts and components can be shielded from the foods or other materials that are being picked and placed to reduce or eliminate such wash-down and clean-up requirements.
Also, in many industrial processes, such as in pick-and-place operations, it is important for robots to exhibit superior range of motion in all directions. Because of its overall design, the end effector of a traditional delta robot has a limited range of motion, in that the end effector does not benefit from any mechanical amplification of movement. Further, superior range of motion in the Z-axis direction is critical for picking products from a conveyor belt and placing them into deep cartons or cases for shipping. As a result of the design of the pivotable arms of the delta robot which extend laterally as they move through their range of motion, often the laterally-extending arms will interfere with placement of products into cartons or cases to such depths. Also, with the delta robot, to obtain incremental increases in range of motion in the Z-axis direction, it is necessary to increase the length of the arms considerably, which adds weight and reduces production cycle time.
For the foregoing reasons, there is room for improvement within the art.